Heat exchangers of the Votator type (A-units) are often very efficient. However, especially when used to cool relatively viscous compositions, the mechanically generated heat can be so high that it counterbalances the cooling capacity of the heat exchanger, as a result of which no cooling of the composition is obtained. Moreover, the shear forces exerted on such viscous compositions by the A-unit can often be undesirably high.
In the preparation of some products, e.g. margarines and shortenings which are to be used to prepare aerated products, it may be desirable to subject the composition after initial plastification by chilling and working, to a heating step to cause a change in the crystal structure to occur. Best results thusfar were obtained by storing the product at about 27.degree. C. for at least 24 hours, before storing it at ambient temperatures. This is, however, an extremely expensive process due to the necessity of keeping a warehouse at a high temperature and due to the substantial amount of handling that is required to ensure that the products are stored in such a way that a fairly homogeneous heating throughout the product is achieved.
It has been proposed to replace the storage at high temperature by a treatment of the product in a microwave oven at the end of the production line. In such a process, however, frequently pressure problems occur, especially when the composition passing through the oven has a relatively high viscosity. The necessity of using high pressures to pass the composition through the production line may result in unacceptable products.